Question

Instruments is reporting all the leaks of this VC in this method. What could be the reason? I think it’s the alloc, but don’t know why is leaking.

- (void)loadViewContent
{
    switch (self.currentView) 
    {
        case 0:
            self.title = @"Title 1";
            [self.navigationItem.backBarButtonItem release]; //para evitar un memory leak
            self.navigationItem.backBarButtonItem = [[[UIBarButtonItem alloc] initWithTitle:@"Blood" style:UIBarButtonItemStylePlain
                                                                                     target:nil action:nil] autorelease];

            [tableContent addObject:@"0"];
            [tableContent addObject:@"1 - 49"];
            [tableContent addObject:@"50 - 75"];
            [tableContent addObject:@"76 - 89"];
            [tableContent addObject:@"More than 89"];
            break;

        case 1: 
            self.title = @"Title 2";
            [self.navigationItem.backBarButtonItem release]; 
            self.navigationItem.backBarButtonItem = [[[UIBarButtonItem alloc] initWithTitle:@"Resp. Rate" style:UIBarButtonItemStylePlain
                                                                                     target:nil action:nil] autorelease];

            [tableContent addObject:@"0"];
            [tableContent addObject:@"1 - 5"];
            [tableContent addObject:@"6 - 9"];
            [tableContent addObject:@"More than 29"];
            [tableContent addObject:@"10 - 29"];
            break;

        default:
            break;
        }
    }

Thanks in advance!

Answer 1

The following code definitely leaks (assuming a memory model of copy or retain on the property tableContent):

self.tableContent = [[NSMutableArray alloc] init];

The setter of tableContent will release the old value and retain / copy / assign the new value. Consider a statement like:

self.tableContent = [NSMutableArray array];

This is perfectly valid because [NSMutableArray array] is an autoreleased object. Subsequent uses of self.tableContent only work after this because the setter of tableContent increments the retain count preventing tableContent from being released.

Your code (as weird as this seems) should be like the following:

self.tableContent = [[NSMutableArray alloc] init];
[self.tableContent release];

OR – requires using an autoreleased object which some devs like to avoid where possible

self.tableContent = [[[NSMutableArray alloc] init] autorelease];

OR – uses an unnecessary temp variable to clarify memory management

NSMutableArray * tempArr = [NSMutableArray alloc];
self.tableContent = tempArr;
[tempArr release];